Effects of Dryness, Moisture Interruption, and Temperature on Germination of Diaporthe citri Pycnidiospores on Yuzu

Melanose caused by Diaporthe citri is a serious disease on yuzu fruits. Moisture is the most important to infect after the pycnidiospores are released. In order to understand how dryness and moisture interruption affect on germination, the conidial suspensions on slide glass were dried for 0-48 h. For the moisture interruption experiment, moisture was supplied for 10 h then interrupted for 0-6 h depending on the treatments. Germinations on the treatments with longer than 15 h of dryness were less than 10%. And those with longer than 3 h of moisture interruption were less than 30%. Compared with other fungal phytopathogens, D. citri was xero-sensitive. Germination on yuzu feel medium was measured under 15, 20, 25, 30, 35°C with 3, 6, 9, 12, 15, 18, and 24 h of wetness. The minimum wetness periods achieving 10% and 50% germinations were 4.5 and 13 h, and the optimum temperatures were 29.1°C and 29.2°C, respectively. From the yuzu medium study, the regression equations to be required wetness period achieving 10% and 50% germinations on various temperatures were Wh₅₀% = 0.1093 × T² - 6.3762 × T + 106.08 and Wh₁₀%=0.082 × T² - 4.8025 × T + 74.861.